How does partially sliding the core into the coil affect inductance?


I understand how the number of turns makes a difference, but I can’t find anywhere what happens(or why) if the core is not fully in. I also didn’t find any circuit diagrams that would at least explain it numerically

In: 4

There’s nothing that really covers sliding the core around because inductance is generally a measured not necessarily predicted value. The exact geometry impacts inductance so you want to test at the end to be sure

What you’re going to end up with is something partway between an air core and an iron core inductor.

Iron core inductors have higher inductance values in the same size, higher losses due to core losses and eddy currents, and if you run too much current through them you’ll max out the field the iron can support and saturate the inductor.

Air core inductors have lower inductance, lower losses, and cannot saturate.

Moving the core in and out is going to change the inductance significantly and potentially cause it to saturate depending on the current levels

Basically, having a material with high permeability gives a bonus to inductance, depending on how much of that material intersects with the actual magnetic field of your coil. Said magnetic field is a torus (donut) shape around your coil – the most effective shape for a ferromagnetic core is thus something like an [EI-frame]( that surrounds the coil in that donut shape and also reaches down through the center – the name comes from the shape of the metal laminations, one is an E-shaped piece and it meets a flat chunk, the I. If you have a setup where the center normally has a ferromagnetic core inserted, then pull the core partway out of the center, some of it is going to reach outside the donut and no longer significantly contribute to increasing the inductance because the magnetic field doesn’t reach it.

The greater the amount of the core in the solenoid, the greater the inductance. This is one of the primary means of making a variable inductor. Turning the terminal increases or decreases the amount of core within the solenoid which varies the inductance appropriately.

Thanks everyone for the replies! I feel somewhat stupid for not thinking that when you remove the core, there’s still air left there